arch/arm/kernel/stacktrace.c

   1 // SPDX-License-Identifier: GPL-2.0-only
   2 #include <linux/export.h>
   3 #include <linux/sched.h>
   4 #include <linux/sched/debug.h>
   5 #include <linux/stacktrace.h>
   6
   7 #include <asm/sections.h>
   8 #include <asm/stacktrace.h>
   9 #include <asm/traps.h>
  10
  11 #if defined(CONFIG_FRAME_POINTER) && !defined(CONFIG_ARM_UNWIND)
  12 /*
  13  * Unwind the current stack frame and store the new register values in the
  14  * structure passed as argument. Unwinding is equivalent to a function return,
  15  * hence the new PC value rather than LR should be used for backtrace.
  16  *
  17  * With framepointer enabled, a simple function prologue looks like this:
  18  *      mov     ip, sp
  19  *      stmdb   sp!, {fp, ip, lr, pc}
  20  *      sub     fp, ip, #4
  21  *
  22  * A simple function epilogue looks like this:
  23  *      ldm     sp, {fp, sp, pc}
  24  *
  25  * When compiled with clang, pc and sp are not pushed. A simple function
  26  * prologue looks like this when built with clang:
  27  *
  28  *      stmdb   {..., fp, lr}
  29  *      add     fp, sp, #x
  30  *      sub     sp, sp, #y
  31  *
  32  * A simple function epilogue looks like this when built with clang:
  33  *
  34  *      sub     sp, fp, #x
  35  *      ldm     {..., fp, pc}
  36  *
  37  *
  38  * Note that with framepointer enabled, even the leaf functions have the same
  39  * prologue and epilogue, therefore we can ignore the LR value in this case.
  40  */
  41 int notrace unwind_frame(struct stackframe *frame)
  42 {
  43         unsigned long high, low;
  44         unsigned long fp = frame->fp;
  45
  46         /* only go to a higher address on the stack */
  47         low = frame->sp;
  48         high = ALIGN(low, THREAD_SIZE);
  49
  50 #ifdef CONFIG_CC_IS_CLANG
  51         /* check current frame pointer is within bounds */
  52         if (fp < low + 4 || fp > high - 4)
  53                 return -EINVAL;
  54
  55         frame->sp = frame->fp;
  56         frame->fp = *(unsigned long *)(fp);
  57         frame->pc = frame->lr;
  58         frame->lr = *(unsigned long *)(fp + 4);
  59 #else
  60         /* check current frame pointer is within bounds */
  61         if (fp < low + 12 || fp > high - 4)
  62                 return -EINVAL;
  63
  64         /* restore the registers from the stack frame */
  65         frame->fp = *(unsigned long *)(fp - 12);
  66         frame->sp = *(unsigned long *)(fp - 8);
  67         frame->pc = *(unsigned long *)(fp - 4);
  68 #endif
  69
  70         return 0;
  71 }
  72 #endif
  73
  74 void notrace walk_stackframe(struct stackframe *frame,
  75                      int (*fn)(struct stackframe *, void *), void *data)
  76 {
  77         while (1) {
  78                 int ret;
  79
  80                 if (fn(frame, data))
  81                         break;
  82                 ret = unwind_frame(frame);
  83                 if (ret < 0)
  84                         break;
  85         }
  86 }
  87 EXPORT_SYMBOL(walk_stackframe);
  88
  89 #ifdef CONFIG_STACKTRACE
  90 struct stack_trace_data {
  91         struct stack_trace *trace;
  92         unsigned int no_sched_functions;
  93         unsigned int skip;
  94 };
  95
  96 static int save_trace(struct stackframe *frame, void *d)
  97 {
  98         struct stack_trace_data *data = d;
  99         struct stack_trace *trace = data->trace;
 100         struct pt_regs *regs;
 101         unsigned long addr = frame->pc;
 102
 103         if (data->no_sched_functions && in_sched_functions(addr))
 104                 return 0;
 105         if (data->skip) {
 106                 data->skip--;
 107                 return 0;
 108         }
 109
 110         trace->entries[trace->nr_entries++] = addr;
 111
 112         if (trace->nr_entries >= trace->max_entries)
 113                 return 1;
 114
 115         if (!in_entry_text(frame->pc))
 116                 return 0;
 117
 118         regs = (struct pt_regs *)frame->sp;
 119         if ((unsigned long)&regs[1] > ALIGN(frame->sp, THREAD_SIZE))
 120                 return 0;
 121
 122         trace->entries[trace->nr_entries++] = regs->ARM_pc;
 123
 124         return trace->nr_entries >= trace->max_entries;
 125 }
 126
 127 /* This must be noinline to so that our skip calculation works correctly */
 128 static noinline void __save_stack_trace(struct task_struct *tsk,
 129         struct stack_trace *trace, unsigned int nosched)
 130 {
 131         struct stack_trace_data data;
 132         struct stackframe frame;
 133
 134         data.trace = trace;
 135         data.skip = trace->skip;
 136         data.no_sched_functions = nosched;
 137
 138         if (tsk != current) {
 139 #ifdef CONFIG_SMP
 140                 /*
 141                  * What guarantees do we have here that 'tsk' is not
 142                  * running on another CPU?  For now, ignore it as we
 143                  * can't guarantee we won't explode.
 144                  */
 145                 return;
 146 #else
 147                 frame.fp = thread_saved_fp(tsk);
 148                 frame.sp = thread_saved_sp(tsk);
 149                 frame.lr = 0;           /* recovered from the stack */
 150                 frame.pc = thread_saved_pc(tsk);
 151 #endif
 152         } else {
 153                 /* We don't want this function nor the caller */
 154                 data.skip += 2;
 155                 frame.fp = (unsigned long)__builtin_frame_address(0);
 156                 frame.sp = current_stack_pointer;
 157                 frame.lr = (unsigned long)__builtin_return_address(0);
 158                 frame.pc = (unsigned long)__save_stack_trace;
 159         }
 160
 161         walk_stackframe(&frame, save_trace, &data);
 162 }
 163
 164 void save_stack_trace_regs(struct pt_regs *regs, struct stack_trace *trace)
 165 {
 166         struct stack_trace_data data;
 167         struct stackframe frame;
 168
 169         data.trace = trace;
 170         data.skip = trace->skip;
 171         data.no_sched_functions = 0;
 172
 173         frame.fp = regs->ARM_fp;
 174         frame.sp = regs->ARM_sp;
 175         frame.lr = regs->ARM_lr;
 176         frame.pc = regs->ARM_pc;
 177
 178         walk_stackframe(&frame, save_trace, &data);
 179 }
 180
 181 void save_stack_trace_tsk(struct task_struct *tsk, struct stack_trace *trace)
 182 {
 183         __save_stack_trace(tsk, trace, 1);
 184 }
 185 EXPORT_SYMBOL(save_stack_trace_tsk);
 186
 187 void save_stack_trace(struct stack_trace *trace)
 188 {
 189         __save_stack_trace(current, trace, 0);
 190 }
 191 EXPORT_SYMBOL_GPL(save_stack_trace);
 192 #endif